This invention relates to production of small containers for pressurized fluids. More specifically, it is the purpose of the invention to provide a small tank formed of multiple side-by-side, basically cylindrical lobes merged in a substantially rectangular overall configuration to provide a small tank having both the strength characteristics of a cylindrical tank and the volumetric capacity of a rectangular tank. Relatively large multi-lobed tanks for the transport of pressurized fluids in marine vessels, or for the land storage of such pressurized fluids are shown and described in Secord U.S. Pat. No. 4,182,254 for "Tanks for the Storage and Transport Fluid Media Under Pressure." It would be desirable to extend this basic technology to enable relatively inexpensive and commercially feasible production of small tanks for pressurized fluids, such as for aerosol dispensers, portable tools and appliances and the like.
It is generally accepted knowledge that the hoop forces generated in a thin walled cylindrical vessel, as a result of internal pressure, are always tensile and tangential, and that the hoop stress in the wall of a cylindrical tank under pressure is proportional to the internal pressure, as well as to the radius of curvature of the cylindrical vessel.
Of course, in the case of a rectangular vessel with planar surfaces, the radius of curvature is infinite and, therefore, the stress is also infinite, even at a very low internal pressure. In actual practice, there is some deflection of the flat surface and the stress is actually finite. However, it is of considerable magnitude, and the ability of a rectangular vessel, or any vessel with flat walls, to withstand internal pressure is minimal. Therefore, tanks for the storage and/or transportation of pressurized fluids are generally made cylindrical or spherical. The multi-lobed vessel illustrated and described in the aforesaid U.S. Pat. No. 4,182,254 provides a means of approaching the volumetric economy of a rectangular tank, while limiting the working stresses of the vessel to that of a cylindrical tank with a modes radius of curvature.
However, the particular pressure vessel illustrated in U.S. Pat. No. 4,182,254 is fabricated by welding plates to X-inserts and Y-inserts and the lobes must be large enough to enable the welder and the inspector to enter them and have sufficient room to perform their respective tasks while inside. In my co-pending application for U.S. Patent Ser. No. 07/324,020 filed Mar. 16, 1989 for "Fabricated Pressure Vessel" there is illustrated and described a small pressure vessel, such as an automotive fuel tank, that is fabricated, as by welding, entirely from the outside.